Ultra-wideband (UWB) is a relatively new term to describe a technology that had been known since the early 1960's as “carrier-free”, “baseband” or “impulse” technology. The transmitted spectrum from a UWB device differs from those of radio, television and radar systems which emit a narrow band signal with bandwidths typically less than 10% of the central frequency, while a UWB spectrum may have a bandwidth of 50% or more of the central frequency. Because of this extremely wide bandwidth, UWB devices have advantages over more traditional systems. They can carry or collect significantly larger amounts of data, operate at much lower power levels, are less susceptible to multi-path interference, and can better penetrate a variety of materials.
The basic concept behind UWB is to generate, transmit, and receive an extremely short duration burst of radio frequency (RF) energy—typically a few tens of picoseconds (trillionths of a second) to a few nanoseconds (billionths of a second) in duration. These bursts consist of one to only a few cycles of an RF carrier wave. The resultant waveforms are extremely broadband, so much so that it is often difficult to determine an actual RF center frequency—thus, the term “carrier-free”. The short pulse duration also allows the radar to ‘see’ at much closer distances and at finer resolutions than more traditional systems.
With its ultra low power pulses, and fine resolution imaging capabilities, the technology can be used for many biomedical applications, such as the fetal monitoring system we are presenting. Statistics have shown that there is a great need for fetal monitoring outside of the hospital environment for at risk pregnancies. There are over 6 million pregnancies resulting in 4.2 million registered births in the United States each year. Of these pregnancies, approximately 10% are classified as high-risk where high-risk denotes an increased incidence of maternal or fetal illness or death or an increased complication rate either before or after delivery. There are a number of conditions or characteristics—known as risk factors, which make a pregnancy high risk. Some of these risk factors are present in the mother-to-be prior to pregnancy, with examples including young or old maternal age, being overweight or underweight, having had problems in previous pregnancies, or pre-existing health conditions, such as high blood pressure, diabetes, or HIV. Other risk factors can develop during pregnancy, including preeclampsia and eclampsia, gestational diabetes mellitus, bacterial vaginosis, bleeding, cholestasis of pregnancy, incompetent cervix, and placenta accrete. Doctors identify and attempt to quantify these factors to determine the degree of risk for a particular woman and baby, allowing the physician to tailor pre- and post-natal care to minimize risk.
There are a variety of procedures available to help quantify the risks and track fetal development. One particular test, the Non-Stress Test (NST), is commonly used to evaluate the fetus' heart rate variability over a finite period of time at regular intervals during pregnancy. A fetal monitor is typically used to measure the fetus' heart rate in response to its movements.
Ultrasonic and electronic fetal heart rate monitoring are commonly used to assess fetal well-being prior to and during labor. Although fetal monitoring allows the detection of fetal compromise or distress, there are also risks associated with currently available and implemented methods of fetal monitoring, including false-positives that may result in unnecessary surgical intervention. Since variable and inconsistent interpretation of fetal heart rate tracings may affect management of a pregnancy, a systematic approach to interpreting the patterns is important.
Fetal heart rate undergoes constant and minute adjustments in response to the fetal environment and stimuli. Fetal heart rate patterns are classified as reassuring, non-reassuring or ominous. Non-reassuring patterns such as fetal tachycardia, bradycardia and late decelerations with good short-term variability typically require intervention to rule out fetal acidosis. Ominous patterns require emergency intrauterine fetal resuscitation and immediate delivery. Differentiating between a reassuring and non-reassuring fetal heart rate pattern is the essence of accurate interpretation, which is essential to guide appropriate triage decisions.
Auscultation of the fetal heart rate (FHR) is performed by external or internal means. External monitoring is performed using a hand-held Doppler ultrasound probe to auscultate and count the FHR during a uterine contraction and for 30 seconds thereafter to identify fetal response. It may also be performed using an external transducer, which is placed on the maternal abdomen and held in place by an elastic belt or girdle. The transducer uses Doppler ultrasound to detect fetal heart motion and is connected to an FHR monitor. The monitor calculates and records the FHR on a continuous strip of paper. Recently, second-generation fetal monitors have incorporated microprocessors and mathematic procedures to improve the FHR signal and the accuracy of the recording. However, it is well-known that existing ultrasonic measurement devices have frequent data dropouts and can cause erroneous measurements to be communicated as accurate assessments of FHR. For example, current ultrasonic FHR systems are known to insert false data suggesting elevated heart rate when, in actuality, the ultrasonic device is simply not picking up any signals for FHR. False data presentation can be caused by shifting of the fetus, the mother or of the sensor by the operator, causing the ultrasonic sensor to lose the signal, effectively creating a non-empirical assessment of FHR which tends to be double the actual FHR. This issue may be exacerbated by the need to ensure that the ultrasound FHR sensor is positioned properly to track the front of the Doppler pressure wave from the fetal heart beat. If the sensor is not properly positioned, it will not collect accurate data.
Internal monitoring is performed by attaching a screw-type electrode to the fetal scalp with a connection to an FHR monitor. The fetal membranes must be ruptured, and the cervix must be at least partially dilated before the electrode may be placed on the fetal scalp. The most important risk of electronic fetal heart rate monitoring is its tendency to produce false-positive results. Electronic fetal heart rate monitoring is associated with increased rates of surgical intervention resulting in increased costs and increased risk of complications to the mother and fetus. Studies show that 38 extra cesarean deliveries and 30 extra forceps operations are performed per 1,000 births with continuous electronic fetal heart rate monitoring versus intermittent auscultation. Variable and inconsistent interpretation of the fetal heart rate tracings by clinicians may affect management of patients. The effect of continuous electronic fetal heart rate monitoring on malpractice liability has not been well established.
Other rare risks associated with EFM include fetal scalp infection and uterine perforation with the intrauterine tocodynamometer or catheter. In light of certain limitations of existing technology, it would be extremely beneficial to provide a sensor capable of noninvasively monitoring fetal heart rate and other fetal indicators which would increase the reliability of measurements, minimize the potential for false-positives of fetal distress, eliminate the possibility of other complications from the monitoring methodology, improve maternal health, provide continuous monitoring to reliably identify normal base-line or reassuring behavior from non-reassuring or ominous behavior, and finally, improve decision making via accurate interpretation to maximize the probability of appropriate triage decisions. In particular, it would be beneficial to provide a sensor less reliant on specific positioning in proximity to the fetus and the fetal heart to ensure accurate FHR readings.
Furthermore, there is also a need to provide monitors capable of determining one or more indicators of maternal health, in addition to fetal health. Current systems and devices typically require multiple devices operating independently to determine one or more indicators of material and fetal health. This process takes additional time, and adds to the complexity of the procedure.
Finally it would be highly beneficial to provide a system for monitoring fetal and/or maternal health via ultra wide band (UWB) that is capable of modulating the power and energy level of the signals applied. Modulation of the applied power level may allow the system to prevent exposing the fetus and mother to unnecessarily high energy levels, as well as regulating the energy needs of the system.
Described herein are methods, devices and systems that may address the needs mentioned above.